1. Field of the Invention
The present invention relates generally to an apparatus for pumping fluids and method for controlling the apparatus.
2. Description of the Related Art
A wide range of pumps have been developed for displacing fluids under pressure produced by electrical drives. For example, in certain fuel injection systems, fuel is displaced via a reciprocating pump assembly which is driven by electric current supplied from a source, typically a vehicle electrical system. In one fuel pump design of this type, a reluctance gap coil is positioned in a solenoid housing, and an armature is mounted movably within the housing and secured to a guide tube. The solenoid coil may be energized to force displacement of the armature toward the reluctance gap in a magnetic circuit defined around the solenoid coil. The guide tube moves with the armature, entering and withdrawing from a pump section. By reciprocal movement of the guide tube into and out of the pump section, fluid is drawn into the pump section and expressed from the pump section during operation.
In pumps of the type described above, the armature and guide tube are typically returned to their initial position under the influence of one or more biasing springs. Where a fuel injection nozzle is connected to the pump, an additional biasing spring may be used to return the injection nozzle to its initial position. Upon interruption of energizing current to the coil, the combination of biasing springs then forces the entire drive assembly to its initial position. The cycle time of the resulting device is the sum of the time required for the pressurization stroke during energization of the solenoid coil, when the drive assembly moves to an actuated position, and the time required for returning the armature and guide to the initial position for the next pressurization stroke. Engine speed is generally a function of the flow rate of fuel to the combustion chamber. Increasing the speed of the engine shortens the duration of each combustion cycle. Thus, a fuel delivery system must provide the desired volumes of fuel for each combustion cycle at increasingly faster rates if the engine speed is to be increased.
Where such pumps are employed in demanding applications, such as for supplying fuel to combustion chambers of an internal combustion engine, cycle times can be extremely rapid. Cycle time refers to the amount of time required for a fuel injector to load with fuel, discharge the fuel into the combustion chamber and then return to its initial position to start the cycle over again. Cycle time is typically short for fuel injectors. For example, injectors used in a direct injection system can obtain a cycle time of 0.01 seconds. That equates to the injectors being able to load with fuel, discharge the fuel into the combustion chamber, and then prepare to reload for a subsequent cycle 100 times in a single second. While this cycle time seems very short, it is often desirable to reduce this time even further when possible.
Moreover, repeatability and precision in beginning and ending of pump stroke cycles can be important in optimizing the performance of the engine under varying operating conditions. While the cycle time may be reduced by providing stronger springs for returning the reciprocating drive assembly to the initial position, such springs have the adverse effect of opposing forces exerted on the reciprocating drive assembly by energization of the solenoid. Such forces must therefore be overcome by correspondingly increased forces created during energization of the solenoid. At some point, however, increased current levels required for such forces become undesirable due to the limits of the electrical components, and additional heating produced by electrical losses.
In high performance engines, such as those used in motorcycles and snowmobiles, the engine speed can reach very high levels, which means very short cycle times. To achieve this, the armature and guide tube need to be returned to their initial position very quickly. This means that the armature and guide tube are returned to their initial position at a relatively high velocity. When the armature impacts the housing at a high velocity, the force of the impact will cause the armature to bounce around, meaning that the force of the impact will cause it to move away from the housing before being pushed back towards the initial position by the biasing force of the spring. This may result in the armature not being in the correct initial position upon the initiation of the following injection event, thus reducing the precision of the injector.
On a different note, the level of noise generated by engines has been lowered considerably over recent years. This causes noises that were not previously audible, especially at low engine speeds, to now be heard. One such noise is the “clicking” sound generated by the injector when the armature impacts the housing upon returning to its initial position. This “clicking” sound can be a disagreement to a person using the engine. That situation would also be problematic in applications where a linearly reciprocating fluid pump is used in other devices generating relatively low noise.
In view of the above-mentioned problems, there is a need not only to control the beginning of the pump stroke cycle but also the ending of the pump stroke cycle in an attempt to ameliorate one or more of the previously mentioned problems.
There is thus a need for an improved technique for pumping fluids in a linearly reciprocating fluid pump. There is a particular need for an improved technique for providing rapid cycle times in fluid pumps while maintaining, and even increasing, the precision of the fluid pump.
There is also a need for a method of reducing the noise generated by a linearly reciprocating fluid pump.